Electrical transmissiion requires a circuit of sorts. How does lightning manage this; it seems that there is only a positive to a negative [earth]. Perhaps the positive and and negative flow occur simoulatneously since the the speed of lightning is at zero or near zero time?

It's quick, but not that quick. There is a delay of the flow of current; more like a half second.

Static electricity.
Is it correct to talk about current ?

You are thinking of things on a visual scale. It works in the same way that things are transferred through a circuit. A circuit is just a pathway of a conductive medium to guide electricity through less conductive media. Electricity always chooses the logical path, and that is along the most conductive route, the easiest for it to travel on. Gold wire conducts electricity excellently.. But Copper does to... So do other metals. Air is less conductive than metal, but still capable of allowing the transfer of electricity. Thats why lightning will more likely hit a tree than the field it is in, because the wet wood and leaves conduct electricity better than the air. Electricity wants to find ground, and if it is strong enough, it will use whatever medium available.

Static electricity.
Is it correct to talk about current ?


Yes its correct to talk about current.

Just like to make state a couple of things:

Originally posted by steponit
it seems that there is only a positive to a negative [earth].

Actually, lightning is conducted through a negatively charged cloud base to a positively charged ground. A positive to negative strike only happens 10% of all storms and have longer flash durations and higher current levels.

Originally posted by SaPhZ
Electricity always chooses the logical path, and that is along the most conductive route, the easiest for it to travel on. Gold wire conducts electricity excellently.. But Copper does to... So do other metals. Air is less conductive than metal, but still capable of allowing the transfer of electricity. Thats why lightning will more likely hit a tree than the field it is in, because the wet wood and leaves conduct electricity better than the air. Electricity wants to find ground, and if it is strong enough, it will use whatever medium available.

In a way you're right. Though technically electricity takes the path of least resistance ... not the most conductive route. All metals conducts electricity because they have very low resistivity coeffcients. Air, on the contrary, has a very high resistivity coefficient. If lightning hits a tree, it's not because the bark is soaked with water. Granted it lowers its resistance to electricity but even the driest wood will get struck by lightning and that's because it shortens the path between the ground and the cloud base.
Lightning is formed in two stages ... the stepped ladder and the return stroke. Simply put, the negative charges from the cloud base "reaches" out to the ground in a series of steps and positive charges from the ground "reaches" out to the cloud base in a similar matter. Since these positive charges want to meet the negative charges due to static attraction, they will take a path that will allow them reach out with the shortest distance possible ... hence off-setting the charge balance of a tree and making it positively charged. This minimizes the resistivity coefficent of air since the path is shortened. When those two opposite charges meet, electrons flow to the ground and a large return stroke surges upward to the cloud along the path followed by the stepped ladder ... creating the lightning effect you see. It's as instantaneous as turning on a light switch.

I see what you mean about visual thinking, SaPhZ.
I was thinking of steponit's original post. To me, the word "circuit" implies a round trip, which lightning is not.
However, I incorrectly equated "circuit" with "current". Thinking of a river, a current can be one-way.
I also confused "static" - i.e. the potential difference between clouds and earth - with the flow (current) of charge that neutralizes that potential.

A lightning bolt does partially neutralize the ground and the cloud but a storm cell continuously creates that potential difference through charge separation within the cell. As long the storm is being maintained by local factors, there will continuously be a charge separation within the cloud base, regardless of the number of electrical discharges. This is explained by a couple of hypothesis about this process which is better explained in my Meteorology textbook.

To singularity"when the opposite charges meet, electronsflow to the ground AND a large return stroke surges upward.. thus lightning instantaneously". That is my question how long a duration is that AND; instantaneously implies no time.

They use the word out of context. It's proabably around a few microseconds for charge travel, depending on distance it needs to travel.

The act of a lightning bolt being created ... whereas a large flow of electrons flow rapidly to the ground and a luminous return stroke surges upward to the cloud... takes one ten-thousandth of a second ... or in better terms, 100 microseconds

Does anyone hear think it would be possible to harness the energy that a lightning bolt gives off?

For that matter, what REALLY happens to the lightning bolt after a cloud-to-ground strike? Air gets ionised, and rapidly expands, thunder is created, reverberating shockwaves, (people are startled), ground surface becomes five times hotter (27,000 degrees Celsius!!) than surface of the sun and the current gets grounded. So much energy is dissipated.

Can't we build a giant capacitor to harness lightness strikes?

And some food for thought: What are the natural generators of lightnings? Some speculate that its probably due to the friction between water/ice droplets and the rapidly-moving air particles that creates a huge static buildup within top and bottom cloud layers.

Originally posted by the greenvision
Can't we build a giant capacitor to harness lightness strikes?


The problem with that is a lightning bolt contains a billion volts at 3,000 amps (on average), or 3 billion kilowatts of power ... and all of that is in 100 microseconds. It's a very voltile discharge and I don't think there is a capacitor that can harness that much power in such a small time frame. If we could ... then it would probably cost more to build one then just building a normal power plant which could supply power for a longer period of time and for cheaper.

Also of note, most of the energy of a lightning bolt is used for other purposes:
... it is impractical to intercept a sufficient number of the lightning strikes occurring in the world, and most of the energy in a lightning strike is converted to thunder, heat, light, and radio waves


Originally posted by the greenvision
And some food for thought: What are the natural generators of lightnings?

The "natural generators" of lightning is through charge separation. However there are two theories on how that is accomplished.

The first one is called the convection process where charges are separated by updrafts and downdrafts. It's a very simple model where positive charges are carried to the cloud tops by updrafts while negative charges are blown to the bottom by downdrafts. The models does explain the distribution of charges within a cloud but doesn't explain things like why charges gather at the -15 C level.

The second theory, which is more accepted, is the precipitation process. Basically it describes ice crystals and hail stones colliding whereas electrical charges are separated and rearranged. The crystals become positively charged and carried upward by updrafts while the hail stones become negatively charged and carried downward by downdrafts ... thus creating a charge imbalance within a cloud. It explains alot about the formation of lightning very well.

how does lightning or any current for that matter know the least resistive path? actually i guess lightning doesn't flow in a straight light to the ground or a tree, it zigzags choosing the least resistive path directly in front of it (so the negative charges reach toward the ground & postive charges to the clouds both taking the least resistive path which should be the same path, connects, then the surge occurs) dont mind me just thinking out loud...


but say in a circuit (those ideal ones from high school) with a current that's entering a node with a resistor in one branch and short cicuit in the other, how does the current know to go through the short circuit and bypass the resistor all together?

TrackerOO,
Think of the water analogy that maybe you have heard of when relating to simple circuits. I've provided a picture of it here:

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/imgele/curlaw3.gif

The constriction of the pipe is basically the bottle neck effect. It creates a "traffic jam" when water goes through the pipe ... or an increase of pressure at the constriction. With the backlog, water will choose an easier path to get to its destination (ie: the least constricted pipe) ... instead of taking the more backed-up path because there is less of an opposing force (the bottle neck) preventing the flow of water. The same goes for electricity and the different resistivity values.

With that water anology,it would suggest that there are alternate pathds which the lightning could take simoultaneously wtih the the "visible" path. It would seem that the lighting would traverse other paths because of the huge flow of ions in the given path, and there fore some some lesser paths would be created to "relieve" this congestion- so it would seem.

I was only using the water analogy to explain TrackerOO's question about a circuit.

For a lightning bolt, it has an "infinte" number of paths in which it can choose from. Though it's path is solely determined by the electric potential gradiant of the air mass. If a parcel of air has the required gradiant of 3 megavolts per meter ... that is required for a step ladder, then it will form within that air parcel instead of a parcel of air with a lower potential gradiant.

You can think of an air parcel with an elec. potential gradiant of lower than 3 megavolts per meter as a very powerful resistor ... though it's not the best way of thinking of it like this since air doesn't behave like a true resistor in a simple circuit.